Recent work in mammalian autonomic ganglia has shown that the number of axons that innervate these nerve cells is correlated with the configuration of the target neurons. Thus, neurons that lack dendrites are innervated by a single axon, whereas neurons that bear dendrites are innervated by a number of axons that is proportional to the complexity of the dendritic tree. These results suggest a novel role for neuronal dendrites, namely that they regulate the degree of convergent innervation of target neurons. They also raise a number of questions about the significance, development and regulation of dendritic arborizations. It is these issues that we now propose to explore. First, we will examine the factors that influence the generation of dendrites in mammalian autonomic ganglia; the purpose of this portion of the project is to understand how dendritic complexity is determined. Second, we will explore the numbers of pre- and postsynaptic nerve cells and the average degree of convergence and dendritic complexity in the cervical sympathetic system of five different mammals; the purpose of this part of the project is to assess the functional significance of different degrees of dendritic complexity and convergence. Third, we will explore the distribution of innervation arising from individual axons on particular target cells in mouse superior cervical ganglion; the purpose of this work is to assess how dendrites influence the apportionment of innervation to neurons more complex than the parasympathetic ganglion cells studied during the initial grant period. In sum, these specific aims are directed at understanding how neuronal dendrites are regulated, how dendrites control convergence, and how convergence influences the function of neural pathways. The reason for pursuing these issues in mammalian autonomic ganglia is that these accessible collections of neurons are simple enough so that some fundamental rules of innervation in the mammalian nervous system may be discerned.